Tube pump for removing dross during galvanizing

ABSTRACT

A tube pump includes a tube having a closed off lower end portion and an open upper end portion. The upper end portion of the tube is adapted to be fastened to support structure. The lower end portion is adapted to be submerged in molten metal. The tube includes an inlet opening and an outlet opening. A pump shaft is adapted to be connected to a motor driven drive shaft and has upper and lower end portions. The pump shaft extends inside the tube. An impeller is fastened to the lower end portion of the pump shaft and disposed near a lower end portion of the tube. Inlet and outlet conduits are connected to the tube inlet and outlet openings adjacent to a top or bottom of the impeller so that a conduit inlet opening is disposed near the surface of the bath and a conduit outlet opening is disposed remote from the conduit inlet opening. The tube pump removes dross from the galvanizing bath to produce galvanized parts having improved properties.

TECHNICAL FIELD

During galvanizing, metal parts are coated with a molten metal to protect the parts against corrosion. However, the presence of dross in the molten metal galvanizing bath can lead to defects and inferior properties of the galvanized part. In an attempt to work around dross problems, the dross can be mechanically removed from the molten metal bath or limited in formation but these are costly approaches.

BACKGROUND OF THE DISCLOSURE

A typical galvanizing process has multiple steps including submerging a part (e.g., a part made of steel), into a degreasing tank then rinsing. Next the part is submerged in a picking bath containing an acidic solution and then rinsed. Next the part is submerged in a fluxing bath and then dried. One example of a flux is zinc ammonium chloride. The flux aids in the process of the liquid zinc wetting and adhering to the steel of the part. The next step is galvanizing by submerging the part in a galvanizing bath of molten metal. The galvanizing bath can be predominantly zinc but may include other metals including lead and aluminum. Optional quenching to reduce the temperature of the coated part may be carried out. Once the part has been immersed in the molten metal and galvanized it is moved out of the bath to another location for cooling and quality inspection.

The molten zinc in the galvanizing bath rapidly oxidizes on the surface of the bath of molten metal. When the steel part is introduced into the melt, a layer of oxidized zinc will attach itself to the leading surfaces of the steel. Since this zinc oxide is the first material the steel touches, this creates an oxide layer against the steel, weakening the coating of zinc on steel and allowing it to more easily chip or flake due to a weak bond with the steel. Even if pure zinc bonds directly with the steel, the addition of the dross creates a brittle section of the coating, causing the material to chip if flexed. If a section of the coating does not remain adhered to the steel part, the benefits of galvanizing are reduced significantly, since the steel will begin to oxidize.

This creates the need for reducing an amount of dross in the galvanizing process. The conventional approaches for avoiding or removing dross are both complicated and expensive. These approaches envelop the entire molten zinc bath in an inert atmosphere or use a robot such as an auto-skimmer to relocate the dross. Another approach, raking the dross away by hand, is extremely dangerous due to risk of severe injuries and is a labor intensive approach to dross removal.

Therefore, there is a need in the industry when performing galvanizing to avoid dross adhering to metal parts. This would increase the final product's coating strength and malleability, due to the removal of impurities, as well as avoiding corrosion in the case of parts that were not completely galvanized with zinc metal.

SUMMARY OF THE DISCLOSURE

In general, a first aspect of the disclosure features a tube pump including a tube comprised of refractory material and having a closed off lower end portion and an open upper end portion. The lower end portion is adapted to be submerged in a bath of molten metal. The tube includes an inlet opening and an outlet opening. The upper end portion of the tube is adapted to be connected to support structure. The upper end portion of the pump shaft is adapted to be connected to a drive shaft of the motor as known in the art. The pump shaft extends inside the tube. An impeller is fastened to the lower end portion of the pump shaft and disposed near a lower end portion of the tube. Inlet and outlet conduits are connected to the tube extending from the tube inlet opening and the tube outlet opening, adjacent to a top or bottom of the impeller, so that an inlet conduit opening is near the surface of the bath and an outlet conduit opening is disposed remote from the inlet conduit opening.

Referring to specific features of the first aspect, the impeller has an auger or screw shape.

Another feature is that the inlet conduit is disposed above the impeller and the outlet conduit is disposed below the impeller. The pump shaft is rotated and its screw threads have a twist direction such that molten metal travels downward upon rotation of the impeller in the refractory tube, which causes molten metal to be drawn from the inlet opening into the impeller and down to the outlet conduit and transferred to the conduit outlet opening, thereby causing the molten metal to have lesser surface dross in a region near the inlet conduit opening.

The system could have another design in which the inlet conduit is disposed below the impeller and the outlet conduit is disposed above the impeller by changing the screw thread twist direction and/or impeller rotation direction to move molten metal upward from the lower inlet conduit, past the impeller and into the upper outlet conduit.

In another feature the inlet conduit, outlet conduit and impeller are comprised of graphite or a ceramic material.

In another feature the outlet conduit extends out of the bath into another vessel for removal of the dross from the molten metal bath.

Another aspect of the disclosure features a tube pump of the first aspect combined with all of the above specific features.

A second aspect of the disclosure is a system for galvanizing metal parts comprising:

-   -   a degreasing bath;     -   an optional rinse station after said degreasing bath;     -   a pickling bath;     -   an optional rinse station after said picking bath;     -   a fluxing bath;     -   a drying station; and     -   a galvanizing bath containing molten metal and the tube pump of         the first aspect above disposed in the galvanizing bath, wherein         operation of the tube pump clears a region of a surface of the         molten metal bath so as to have reduced dross at a location of         the inlet opening;     -   a mechanism for placing the part inside the galvanizing bath in         a region of the inlet opening of the inlet conduit, and for         removing the part from the galvanizing bath, effective to         produce a metal galvanized part with reduced defects, lesser         corrosion and/or higher strength.

The tube pump has various advantages. One advantage is that it presents an economical and efficient way to produce cleaner galvanized parts. No costly dross removing robot or inert gas enclosure are required. Another advantage is that fewer parts are used in that a submergeable base containing a volute chamber is not needed, nor are posts for securing the base to the motor mount. A tube pump is susceptible to the influences of torque since it contains a rapidly rotating impeller that can pump in different directions. Since in the device of this disclosure flow is directed downwards into the inlet conduit, lateral torque on the tube is reduced such that the single tube can contain the forces of the pump, reducing complexity and component material to successfully create this pump. The locations of the inlet and outlet conduits can also be adjusted so as to minimize the torque on the tube pump.

The unique impeller design as a screw or auger shape allows pumping predominantly vertically instead of to the side, unlike a traditional impeller that pumps to the side. This gives two benefits. The downwards pumping direction allows a “zero-head” scenario, where the inlet and outlet of the pump are essentially level, or the outlet is slightly below the inlet. This means there is no pressure barrier to overcome in order to pump, increasing overall flow rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a galvanizing line including a galvanizing bath which can receive the pump of the present disclosure;

FIG. 2 is perspective view of the galvanizing bath of the present disclosure; and

FIG. 3 is a cross-sectional side view of an impeller, inlet and outlet conduits according to the present disclosure.

DETAILED DESCRIPTION

A tube pump 10 is suitable for use in removing dross during galvanizing and includes a tube 12 12 comprised of refractory having a closed off lower end portion 14 and an open upper end portion 16. The lower end portion 14 of the tube 12 is adapted to be submerged in a bath of molten metal M. The galvanizing bath and the other baths are contained by enclosures, for example, the galvanizing bath is surrounded by refractory brick as known in the art. Support structure 18 is disposed outside of the molten metal bath for securing the upper end portion of the tube 12. The tube includes an inlet opening and an outlet opening (shown by 20, 22 in either upper or lower position). The position of the inlet and outlet openings can be reversed. A motor (not shown) is mounted to the support structure and includes a drive shaft (not shown). A pump shaft 24 is comprised of refractory material having upper and lower end portions 26, 28, respectively. The upper end portion 26 of the pump shaft 24 is connected to the motor's drive shaft in a manner known in the art. The pump shaft 24 extends centered inside the tube 12. An impeller 30 is fastened to the lower end portion 28 of the pump shaft 24 and is disposed near the lower end portion 14 of the tube 12. An inlet conduit 32 has one end portion 34 connected to the inlet opening 20 of the tube 12 adjacent to a top of the impeller 30 and an inlet end portion 36 with an inlet opening 38 disposed near and below a surface of the bath of molten metal M. An outlet conduit 40 has one end portion 42 connected to the outlet opening 22 of the tube 12 adjacent to bottom of the impeller and another end portion 44 including an outlet opening 46 remote from the inlet opening 38.

The impeller 30 has an auger or screw shape. In one aspect, the inlet conduit 32 is disposed above the impeller. The outlet conduit 40 is disposed below the impeller. The pump shaft rotates in a direction such as shown by the arrows and the impeller screw has a screw direction as seen in FIG. 2 such that molten metal travels downward upon rotation of the impeller in the tube. This causes molten metal to be drawn from the tube inlet opening 20 into and through the screw threads of the impeller 30 and down to the tube outlet opening 22 and transferred through the outlet opening 46, thereby causing the molten metal to have lesser surface dross in a clear region C (e.g., as shown by dotted lines) near the conduit inlet opening 38.

The inlet conduit 32 above the impeller extends to near the surface of the molten metal, drawing the top portion of the molten metal bath into the pump. The outlet conduit 40 below the impeller can be located below the surface of the metal, allowing the dross to float back to the top and to be manually skimmed in a deposit region D (e.g., as shown by dotted lines in FIG. 2) more convenient for a worker to access. Alternatively, the outlet conduit 40 can extend out of the bath into a sow or other transfer system for removal (dotted portion 40′). The system of this disclosure is designed for clearing away surface dross or floating dross but will clear away any material in the clearing region C.

Referring more specifically to the impeller and to FIG. 3, the impeller 30 is a solid body containing a threaded central opening 48 on one end for receiving the threaded end of the pump shaft 50. The impeller has screw threads 52 extending from an upper end portion 54 toward a lower end portion 56 on a side of the impeller. The impeller screw threads extend in a twist direction as viewed from above the impeller. In this application the screw threads can be disposed so as to twist downwardly in the counterclockwise direction from a perspective view. This impeller is rotated clockwise when the impeller is viewed from above to achieve downward flow of molten metal. In another variation the screw threads of the impeller twist in an upward counterclockwise direction from a perspective view. The impeller is rotated clockwise from a top view and molten metal flows upwards. In this case the upper conduit above the impeller is the outlet conduit and the lower conduit below the impeller is the inlet conduit.

Referring to FIG. 1, a system for galvanizing metal parts P (e.g., steel fences) is shown including a degreasing bath 58 and an optional rinse station 60 after the degreasing bath. Next is a pickling bath 62 containing acid for treating the metal part and an optional rinse station 64 after the picking bath. Next is a fluxing bath 66 and an optional drying station 68. A galvanizing bath 70 contains the molten metal M and the tube pump shown in FIG. 2 disposed in the galvanizing bath 70. Operation of the tube pump clears a region C of a surface of the molten metal bath so as to have reduced dross at a location of the inlet opening. It will be appreciated that the size and shape of the cleared region C of molten metal is variable as with the speed of rotation of the pump shaft and location of the inlet conduit (and so is the size and shape of parts variable), and that the part would be positioned so as to be suitably contained within the cleared region C. A mechanism 72, such as the hoist shown, places the metal parts P (fence portions in this example) inside the galvanizing bath in the cleared region C near the inlet opening of the inlet conduit, and removes the part P from the galvanizing bath, effective to produce a galvanized part 74 with reduced defects, lesser corrosion and/or higher strength. 

What is claimed is:
 1. A tube pump that is suitable for use in removing dross during galvanizing, comprising a tube having a closed lower end portion and an open upper end portion, said lower end portion being adapted to be submerged in molten metal, said upper end portion of said tube being adapted to be fastened to support structure outside of a molten metal bath, said tube including an inlet opening and an outlet opening; a pump shaft having upper and lower end portions, said upper end portion of said pump shaft being adapted to be connected to a motor drive shaft, and said pump shaft extending inside said tube; an impeller fastened to the lower end portion of said pump shaft and disposed near a lower end portion of said tube; an inlet conduit having one end portion connected to the inlet opening of said tube adjacent to a top or bottom of said impeller and an inlet end portion with an inlet opening disposed near a surface of the bath; an outlet conduit having one end portion connected to the outlet opening of said tube adjacent to a top or bottom of said impeller and an outlet end portion remote from the inlet opening of said inlet conduit.
 2. The tube pump of claim 1 wherein said impeller has an auger or screw shape.
 3. The tube pump of claim 1 wherein said inlet conduit is disposed above said impeller and said outlet conduit is disposed below said impeller, and said pump shaft is rotated and its screw threads have a twist direction such that molten metal travels downward upon rotation of said impeller in said refractory tube, which causes molten metal to be drawn from said inlet opening into said impeller and down to said outlet conduit and transferred to the outlet opening, thereby causing the molten metal to have lesser surface dross in a region near the inlet opening.
 4. The tube pump of claim 1 wherein said tube, said pump shaft, said inlet conduit, said outlet conduit and said impeller are comprised of graphite or a ceramic material.
 5. The tube pump of claim 1 wherein said outlet conduit extends out of the molten metal bath into another vessel for removal of the dross from the molten metal bath.
 6. The tube pump of claim 1 wherein said inlet conduit and said outlet conduit are so close to said impeller that said pump effectively operates with zero head increasing pumping efficiency.
 7. A tube pump that is suitable for use in removing dross during galvanizing, comprising a tube including a closed lower end portion and an open upper end portion, the lower end portion being adapted to be submerged in molten metal and the upper end portion adapted to be fastened to support structure, and an inlet opening and an outlet opening; a pump shaft having upper and lower end portions, the upper end portion of said pump shaft being connected to a motor driven drive shaft, and said pump shaft extends inside said tube; an impeller fastened to the lower end portion of said pump shaft and disposed near a lower end portion of said tube, wherein said impeller has an auger or screw shape; an inlet conduit having one end portion connected to the inlet opening of said tube adjacent to a top or bottom of said impeller and an inlet end portion with an inlet opening disposed near a surface of the bath; an outlet conduit having one end portion connected to the outlet opening of said tube adjacent to a top or bottom of said impeller and an outlet end portion remote from the inlet opening of said inlet conduit; wherein said tube, said impeller, said pump shaft, said inlet conduit, and said outlet conduit are comprised of graphite or a ceramic material; wherein said inlet conduit is disposed above said impeller and said outlet conduit is disposed below said impeller, and said pump shaft is rotated in a direction and its screw threads have a twist direction such that molten metal travels downward upon rotation of said impeller in said tube, which causes molten metal to be drawn from said inlet opening into said impeller and down to said outlet conduit and transferred to the outlet opening, thereby causing the molten metal to have lesser surface dross in a region near the inlet opening.
 8. A system for galvanizing metal parts comprising: a degreasing bath; an optional rinse station after said degreasing bath; a pickling bath; an optional rinse station after said picking bath; a fluxing bath; a drying station; and a galvanizing bath containing molten metal and said tube pump of claim 1 disposed in said galvanizing bath, wherein operation of said tube pump clears a region of the molten metal near the inlet opening so as to have reduced dross; a mechanism for placing said parts inside said galvanizing bath in the clear region of the molten metal and for removing said parts from said molten metal bath, wherein said tube pump operation produces metal galvanized parts with reduced defects, lesser corrosion and/or higher strength. 